Check for IPv6 address master_uri address

Using runnerClient.master_call via client/api.py in an IPv6 environment results in the following error:
  File "/usr/lib/python2.7/dist-packages/salt/payload.py", line 172, in __init__
    self.socket.connect(master)
  File "socket.pyx", line 459, in zmq.core.socket.Socket.connect (zmq/core/socket.c:4228)
ZMQError: Invalid argument

The reason for the error is the missing IPv6 brackets in master_uri as created within salt/config.py.